Heretofore, dielectric ceramics have been widely used in dielectric resonators, dielectric substrate materials for MIC and waveguides that are used in high-frequency applications such as microwave and millimeter waves. With the recent development and spread of mobile communication including portable telephone, demand for dielectric ceramics as materials for electronic circuit boards and electronic parts has been increasing.
As a dielectric ceramic composition for electronic circuit boards and electronic parts, there have been developed so-called glass ceramics made of glass, which can be fired together with a high-conductive metal such as silver or copper, or a composite material of glass and ceramics.
For example, Unexamined Patent Publication (Kokai) No. 2001-348268 describes a dielectric ceramic composition comprising SiO2, CaO, MgO, B2O3 and Al2O3 which can be fired at the temperature of 1000° C. or lower and can be used in high-frequency parts.
Although the dielectric ceramic composition described in Unexamined Patent Publication (Kokai) No. 2001-348268 exhibits low dielectric loss, a temperature coefficient of electrostatic capacity increases because the dielectric ceramics has a large temperature coefficient of resonant frequency, and thus desired electric conductive characteristic can not be obtained according to service environment. Because of a low mechanical strength, cracking is likely to be caused by impact of an electronic equipment using the dielectric ceramics upon dropping.